It all started in 1995, when friends Casey Dean and Eduard Nitz went out to grab some food from a McDonald's chain in Adelaide, Australia. One of their friends didn't eat their burger, asking them to "hold on to this for next time."

Consequently, Nitz kept it locked away for safekeeping in a wooden box until the pal came back for his meal, which he never did.

The burger has maintained its "good looks" by simply being kept in the box. Consequently, the burger has dried out with a "rock hard" texture, according to a recent interview with Dean and Nitz for "The Project," a talk show on Network Ten, Australia.

What started off as a joke has now turned into a social media phenomenon and a charitable campaign.

The two Aussies have now capitalized on this vintage delicacy by setting up website Senior Burger where you can download the official song "Free the Burger" by The Pentagonal Diagonals and buy merchandise. Proceeds from the song and gift sales go to Beyond Blue, a national initiative in Australia to raise awareness on anxiety and depression.

Kanye loves a burger

To spur further interest and preserve its legacy, the dynamic duo have now added a special celebrity face: Kanye West. A logo of the American rapper biting into a burger is used on T-shirts, throw pillows, leggings and iPhone/Samsung Galaxy phone cases.

Dean told CNBC via email that "the campaign is going amazingly well! The story has been on every national TV and radio station in Australia and hundreds around the globe. The single 'Free The Burger' is going crazy on iTunes and the merch is selling like mad!"

"We couldn't be more amazed/happier about how things have turned out, but at the end of the day we can raise some money for a great cause," Dean added.

In terms of the future of the burger's legacy, Dean told CNBC that "We're currently chatting to Guinness book of records about getting a place in their book and we'd like to go on a world tour to get people to think more about what they put into their body."

Dean added that "everyone has asked us to eat it but we consider it to be our little solid friend, and you don't eat your friends."